Note: Descriptions are shown in the official language in which they were submitted.
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WIRELESS PROCESS FIELD DEVICE DIAGNOSTICS
BACKGROUND OF THE INVENTION
The present invention relates to industrial
process control or monitoring systems. More
specifically, the present invention relates to
wireless process field devices used in such systems.
In industrial settings, control systems are
used to monitor and control inventories of industrial
and chemical processes, and the like. Typically, the
control system that performs these functions uses
field devices distributed at key locations in the
industrial process and coupled to control circuitry
in the control room by a process control loop. The
term "field device" refers to any device that
performs a function in a distributed control or
process monitoring system, including all devices used
in the measurement, control and monitoring of
industrial processes.
Some field devices include a transducer. A
transducer is understood to mean either a device that
generates an output signal based on a physical input
or that generates a physical output based on an input
signal. Typically, a transducer transforms an input
into an output having a different form. Types of
transducers include various analytical equipment,
pressure sensors, thermistors, thermocouples, strain
gauges, flow transmitters, positioners, actuators,
solenoids, indicator lights, and others.
Typically, each field device also includes
communication circuitry that is used for
communicating with a process controller, other field
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devices, or other circuitry, over the process control
loop. In some installations, the process control loop
is also used to deliver a regulated current and/or
voltage to the field device for powering the field
device. The process control loop also carries data,
either in an analog or digital format.
Traditionally, analog field devices have
been connected to the control room by two-wire
process control current loops, with each device
connected to the control room by a single two-wire
control loop. Typically, a voltage differential is
maintained between the two wires within a range of
voltages from 12-45 volts for analog mode and 9-50
volts for digital mode. Some analog field devices
transmit a signal to the control room by modulating
the current running through the current loop to a
current proportional to the sensed process variable.
Other analog field devices can perform an action
under the control of the control room by responding
to the magnitude of the current through the loop. In
addition to, or in the alternative, the process
control loop can carry digital signals used for
communication with field devices. Digital
communication allows a much larger degree of
communication than analog communication. Field
devices that communicate digitally can respond to and
communicate selectively with the control room and/or
other field devices. Further, such devices can
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provide additional signaling such as diagnostics
and/or alarms.
In some installations, wireless
technologies have begun to, be used to communicate
with field devices. Wireless operation simplifies
field device wiring and setup. Wireless installations
are currently used in which the field device includes
a local power source. For example an internal battery
(potentially charged by a solar cell) or other
technique to obtain power without any wired
connection. However, the various components and
systems which are used to make a field device
"wireless" are- also susceptible to degradation and
failure. This can introduce errors in measurements
or control of an industrial process and can even lead
to complete failure of a process device.
SUMMARY OF THE INVENTION
A wireless process variable transmitter for
use in an industrial process control or monitoring
system includes a process variable sensor configured
to sense a process variable of the industrial process.
A power source is configured to power the process
variable transmitter. Diagnostic circuitry diagnoses
operation of the process variable transmitter and
provides a diagnostic output. Wireless communication
circuitry transmits information related to the sensed
process variable and related to the diagnostic output
over a wireless communication link.
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According to an aspect of the present invention, there
is provided a wireless process variable transmitter for use
in an industrial process control or monitoring system
comprising:
a process variable sensor configured to sense a
process variable of the industrial process;
a power source configured to power the process
variable transmitter without a wired connection to an
external source of power;
diagnostic circuitry configured to diagnose operation
of the power source of the process variable transmitter and
having a diagnostic output indicative of an impending
failure of the power source;
wireless communication circuitry configured to
transmit and receive information related to the sensed
process variable and related to the diagnostic output over
a wireless communication link; and
wherein the power source includes a solar cell and
wherein the diagnostic circuitry monitors a voltage output
of the solar cell.
According to another aspect of the present invention,
there is provided a method for diagnosing a wireless
process transmitter coupled to an industrial process
comprising:
powering the wireless process transmitter with a power
source which includes a solar cell without a wired
connection to an external source of power;
diagnosing operation of the power source of the
wireless process transmitter by monitoring a voltage output
of the solar cell, the diagnostics indicative of an
impending failure of the power source; and
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transmitting information related to a diagnoses of the
power source of the wireless process transmitter over a
wireless communication link.
According to a further aspect of the present
invention, there is provided a wireless process variable
transmitter for use in an industrial process control or
monitoring system comprising:
a process variable sensor configured to sense a
process variable of the industrial process;
a power source configured to power the process
variable transmitter;
diagnostic circuitry configured to diagnose operation
of the power source of the process variable transmitter and
having a diagnostic output indicative of a condition of the
power source;
wireless communication circuitry configured to
transmit and receive information related to the sensed
process variable and related to the diagnostic output over
a wireless communication link;
wherein the power source includes a solar cell and
wherein the diagnostic circuitry monitors a voltage output
of the solar cell;
the power source includes a battery; and
the diagnostic circuitry provides an output related to
a time period required to charge the battery.
According to a further aspect of the present
invention, there is provided a wireless process variable
transmitter for use in an industrial process control or
monitoring system comprising:
a process variable sensor configured to sense a
process variable of the industrial process;
a power source configured to power the process
variable transmitter;
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diagnostic circuitry configured to diagnose operation
of the power source of the process variable transmitter and
having a diagnostic output indicative of a condition of the
power source;
wireless communication circuitry configured to
transmit and receive information related to the sensed
process variable and related to the diagnostic output over
a wireless communication link;
wherein the power source includes a solar cell and
wherein the diagnostic circuitry monitors a voltage output
of the solar cell;
the power source includes a battery; and
a MOSFET which couples the battery to the circuitry
configured to prevent discharge of the battery.
According to a further aspect of the present
invention, there is provided a method for diagnosing a
wireless process transmitter coupled to an industrial
process comprising:
powering the wireless process transmitter with a power
source which includes a solar cell;
diagnosing operation of the power source of the
wireless process transmitter by monitoring a voltage output
of the solar cell;
transmitting information related to a diagnoses of the
power source of the wireless process transmitter over a
wireless communication link;
the power source includes a battery; and
providing an output related to a time period required
to charge the battery.
According to a further aspect of the present
invention, there is provided a method for diagnosing a
wireless process transmitter coupled to an industrial
process comprising:
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powering the wireless process transmitter with a power
source which includes a solar cell;
diagnosing operation of the power source of the
wireless process transmitter by monitoring a voltage output
of the solar cell;
transmitting information related to a diagnoses of the
power source of the wireless process transmitter over a
wireless communication link;
the power source includes a battery; and
providing an output related to battery temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
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Figure 1 is a simplified block diagram
showing a process control or monitoring system for
use with the present invention.
Figure .2 is a block diagram showing
components in a field device of the present
invention.
Figure 3 is a more detailed block diagram
showing components of the field device of figure 2.
Figure 4 is a block diagram showing example
steps for implementing the present invention.
DETAILED DESCRIPTION
The present invention includes diagnostics
for a wireless field device of the type which is
designed to wirelessly communicate with a remote
location such as a control room, hand held device or
the like. As discussed in the Background Section it
is often useful to couple sensor measurements and
self-powered wireless communication techniques
together to eliminate needs for long wire runs and
process installations. One known method for providing
local power for the combination of a sensor and
wireless communication device is to use a solar panel
to convert sunlight into power. Typically, a battery
is also used with the system to provide power storage
so that the unit can operate while sunlight is not
present. Other techniques can also be used to power
the device without requiring a wired connection.
Field devices are typically mounted in a
remote location. The present invention includes the
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recognition that it is desirable to provide
diagnostic capabilities directed to the wireless
features of the field device, and to other aspects of
the field device. This allows the cause of potential
failures to be detected. Further, in some
configurations, the diagnostic capabilities are used
to assist in the mounting and configuration of the
field device during installation. If a failure is
detected, the diagnostic capabilities of the device
can be used to report a probable cause or source of
the failure. The diagnostic information can also be
used to compensate for the failure.
Figure 1 is a simplified diagram showing an
example process control or monitoring system 10 which
includes a control room or control system 12 coupling
to field devices 14 and 16. Field device 14 is shown
coupled to process piping 18 and field device 16 is
shown coupled to storage tank 20. Devices 14 and 16
include antennas 22 and 24, respectively, for
transmitting and/or receiving information from
antenna 26 associated with process control circuitry
13 of process control room 12. Devices 14 and 16
communicate using wireless radio frequency (RF)
communication links 28 and 32 with circuitry 13 in
control room 12. Field devices 14 and 16 include
components to provide local power to the devices
without requiring running additional wires. For
example, device 14 and 16 can include solar cells
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and/or batteries for local power as illustrated below
in greater detail.
These additional components which are used
to eliminate the needs for wires to devices 14 and 16
can be a source of potential failure. The present
invention provides a technique to provide diagnostic
capability in field devices that use wireless
communication techniques and a self-contained power
source. For example, a field device can include one
or more sensors for measuring a process variable and
be coupled to a solar panel/storage battery power
source. The device communicates over a wireless
communication link including, for example, to a cell
phone and/or GPRS (General Packet Radio System). In
one specific example, the field device can include a
supervisory digital control capability that can be
used to manage the power by causing the wireless
communication circuitry (and the process variable
generator) to enter a sleep mode when not active. The
same circuitry can be used to execute algorithms for
use in diagnosing components of the device, including
the components used to provide the wireless
capabilities of the device.
Figure 2 is a simplified block diagram
showing field device 14 shown in figure 1 in greater
detail. Field device 14 includes an actuator or
transducer 30, wireless input/output (communication)
circuitry 32, diagnostics 34, power supply circuit
36, battery 38 and solar panel 40. The
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actuator/transducer 30 can be either a sensor used to
sense a process variable or an actuator, such as a
valve, which is used to control a process. The
wireless communication circuitry 32 couples to
antenna 22 for communication with circuitry 13 (not
shown in Figure 2) of control system 12 over its
antenna 26. Power supply circuit 36 is used to
provide power to circuitry within field device 14.
The power supply circuitry 36 can operate using power,
received from solar cell 40 or power received from
battery 38. The power supply circuitry 36 can be
powered from any type of power source that does not
require wiring to a remote power source. The power
supply circuitry 36 can be self contained within the
field device 14 or, in some embodiments be located
externally to the field device and positioned
proximate to the field device. For example, a solar
powered unit can be used to power a transmitter or
other field device over a two wire connection which
is also used to carry information. In such a
configuration, the power supply circuitry can also
provide wireless communication to a remote location.
Such configurations are shown and described in U.S.
patent application Serial No. 10/850,828, WIRELESS
POWER AND COMMUNICATION UNIT FOR PROCESS FIELD DEVICES
filed on May 21, 2004 which is hereby incorporated by
reference in its entirety. If sufficient power is
received from solar cell 40, power supply circuitry
36 can also be used to charge the battery 38. The
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block 34 labeled diagnostics is used to implement the
diagnostic functions in accordance with the present
invention as discussed below in more detail. This
diagnostic function can be implemented in hardware
components, software components, or a combination of
components and, for simplicity, it is shown as a
single block 34 in figure 2.
Figure 3 is a more detailed block diagram
of process device 14 and shows a process variable
sensor 50. The process variable sensor may be
positioned within the housing of device 14 or
external to the housing as illustrated in figure 3.
Measurement circuitry 52 couples to process variables
sensor 50 and is used to perform initial signal
processing prior to providing a measurement signal to
controller 58. An optional user input 54 is shown as
operator button in figure 3. Similarly, an optional
output device such as LCD display 56 is shown.
Controller 58 is typically a microprocessor
based controller and couples to a memory 60 and a
clock 62. The clock 62 determines the operational
speed of digital circuitry within field device 14 and
memory 60 is used to store information. Memory 60
can comprise both permanent and volatile memory and
can be used to store data used during processing,
programming instructions, calibration information, or
other information, data or instructions for use with
process device 14. In the configuration of figure 3,
the diagnostic function 34 illustrated in figure 2
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can be implemented, for example, within controller
58, and with optional additional circuitry as
required.
Figure 4 is a simplified block diagram
showing steps in accordance with the diagnostic
algorithm of the present invention. Figure 4
illustrates block diagram 100 which is initiated at
start block 102. At block 104, the diagnostic test
or algorithm is initiated as described below in more
detail. Subsequent processing of the diagnostic
result can be performed at block 106, as desired. An
output, or other step, is performed at block 108
based upon the result of the diagnostic test. if
desired, the diagnostic test can be repeated at block
110. For example, the diagnostic test can repeat at
periodic or other desired intervals, or upon
initiation from the detection of an event sensed in
the process, or upon receipt of a command, or other
cause to initiate diagnostics. The diagnostic
processing optionally stops' at block 112. The steps
illustrated in figure 4 can be implemented, for
example, by controller 58 based upon a program stored
in memory 60.
The diagnostic test provided by block 104
can be any diagnostic related to the wireless
functionality of device 14 including the wireless
communication ability of device 14, the power supply
capabilities of device 14 such as power supply
circuit 36, solar cell 40 and/or battery 38. Further,
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in some configurations, the diagnostics are performed
on any aspect of device 14 or of system 10.
In one example, an additional sensor 59
shown in Figure 3 is used to provide diagnostic
information. For example, a voltage sensor can be
included in device 14 to sense the voltage output
from solar cell 40. If the open circuit voltage of
solar panel 40 over an extended period, for example
24 hours, is below a threshold voltage, the
diagnostic test 104 can provide an output indicating
that the solar panel 40 is blocked or broken. In
another example, the maximum power output of the
solar panel 40 is measured by sensor 59 and used to
make a determination regarding the available solar
energy. Sensor 59 can comprise temperature sensor
coupled to solar panel 40 which is used to sense
temperature of the panel 40 directly. The sensed
temperature can be compared with the threshold to
identify an over-temperature occurrence.
In another example configuration, the
controller 58 uses sensor 59 to monitor a maximum or
a total power output from the solar panel 40 over a
period of time, such as a number of days. This
actual power output can be compared to actual power
usage of device 14 such that an output from
controller 58 can be indicative that the installation
can not support the power required by the operation
of device 14. The data can also be used to determine
the amount of available power remaining during normal
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operation or the amount of time to fully charge the
battery 38. An output can be provided which indicates
that the power budget criteria for the device is, or
is not, being met. The time period required to fully
charge the battery 38 can be measured and an alarm
output provided if the required time period is
greater than a desired threshold. Further, the
controller 58 can provide an output reporting the
percent equivalent sun hours (time period) per day
for a particular installation, or provide an output
indicating that a relatively small amount of power
has been provided by solar panel 40 over a period of
time, for example due to shading.
Additionally, using sensor 59, the
diagnostic functionality can be configured to monitor
voltage and/or current draw, for example, from
battery 38 and/or solar panel 40 and report back
information such as the average and peak power
requirements of the device 14. Significant changes
in daily power requirements can be reported or used
to identify a fault condition. The rate of charge of
the battery 38 can be used to diagnose operation, for
example, if the battery 38 charges at a much slower
rate or fails to reach full charge over a specified
time or power level. An indication can be provided
that the battery 38 may fail and should be replaced.
The remaining battery life can be determined, for
example, based upon the maximum discharge levels,
temperature history and frequency, a decrease in
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charge rates, or using other criteria. Excessive
battery temperatures can also be monitored.
The power supply circuitry 36 can also be
monitored by sensor 39 to identify a failed or
failing component. For example, if the charging
circuit does not charge the battery, despite a
dropping battery voltage, a failure can be indicated.
Variations in voltage levels or signals can be used
to indicate corroded terminals, a bad battery, or bad
charging circuitry. Similarly, the charging
circuitry or the power supply circuitry 36 can
completely bypass the charging of battery 38 and
provide all available power to circuitry within
device 14.
In another example, a blocking device 70 is
used to prevent the battery 38 from discharging back
into the power supply circuitry 36. The blocking
device 70, for example, can be contained within power
supply circuitry 36 and can comprise a diode.
However, if a diode is employed, a voltage drop of
0.7 volts occurs across the component. However, if a
MOSFET transistor is employed rather than a diode or
the like, the 0.7 volt drop will not be apparent and
additional power will be available for charging of
the battery 38 or for use with other circuitry.
In another example, the diagnostic test 104
is used during mounting and installation of the
device 14. Such a mode can be entered, for example,
using a remote RF transmitter, or by providing an
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input through input 54. For example, the signal
strength received by the antenna 22 can be monitored
such that the antenna can be oriented properly for
maximum signal strength. A warning can be provided
if the signal strength is insufficient for reliable
operation. Similarly, the output from the solar
panel 40 can be monitored and this information used
in orienting the solar panel 40 relative to the sun
for maximum efficiency. An output can be provided
which indicates the condition of the battery so that
an operator is ensured that a "good" battery is being
used in the installation. Battery temperature can
also be monitored using sensor 59. During
installation, the diagnostic tests can verify for
example, that the battery polarity, solar panel
polarity, and charging circuitry are all functioning
properly. In another example, test process variable
values measured with the process variable sensor 50
and can be sent to the control room for verification.
Other information such as operating parameters and
functional test results can also be sent to the
control room or other remote location. In another
example, the span and zero settings of the process
device 14 are sent over the wireless link both before
and after calibrating the device 14. The after
calibration values can be stored as a reference. The
value of the last calibration can be transmitted, or
displayed on the local display.
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In another aspect, optical site diagnostics
are used to verify conditions of the installation.
For example, an image capture device 74, such as a
digital camera or the like, can be used to capture
images of the process device 14, or components of the
device 14. This image information is used to verify
the condition of the solar panel 40 and the mounting
arrangement of the solar panel 40. For example, the
image can indicate whether the solar panel 40 has
become detached, broken or vandalized. Further
still,, this information can be used to provide a
visual verification that the device 14 is being
serviced or repaired by an operator, or a visual
indication of weather indications.
The configuration and capabilities of the
diagnostic functionality of the present invention
provide a number of advantages for use with field
devices having self contained power sources. These
techniques provide a means of remotely assessing the
condition and functionality of a process variable
transmitter and self contained power generation unit.
The installation and site conditions required for
proper unit operation can be verified. Additional
diagnostic capabilities can be added for subsequent
operations. Information can be provided locally, for
example to an installation technician, such that the
technician is able to verify that the installation
and site conditions will allow proper unit operation
and the device can be adjusted accordingly. Image
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information can also be provided and used for
diagnostics. For example, images can be transmitted
over the wireless communication link for us in
diagnosing or verifying device operation or
condition.
Although the present invention has been
described with reference to preferred embodiments,
workers skilled in the art will recognize that
changes may be made in form and detail without
departing from the spirit and scope of the invention.
The various circuits and algorithms and functionality
can be implemented in hardware, software or their
combination. Various components of the present
invention can be implemented across a number of
different components. For example, a particular
diagnostic function may be implemented partially in a
microprocessor and/or partially in other components
such as measurement circuitry, memory, software, etc.
Although a solar cell and battery have been described
herein, the present invention is applicable to other
components used for powering a wireless device. As
used herein, "self contained power source" refers to
apparatus to power the process device without
requiring a physical connection to a remote power
source. The diagnostics can be initiated
automatically, or, upon receipt of a command of other
.event such as through input 54.
